I would keep 3.8.11 and just use add-ons and tweak it here and there. We were running 3.5 up until last year. People generally don't like change. It's the members who make for a great community, not necessarily the software. As they say at oldversion.com, newer is not always better.

I like your simple, old school layout. It's very easy to navigate.

Your site seems very fast. 30GB is a lot of memory. Who is your host and what price range are you paying for it monthly if you don't mind me asking?